What do you consider to be long? I do five seconds at full pressure for water backflush, ten seconds for the first Purocaffe flush and then five seconds each for the followup flushes. The cheap original Ulka vibe pump on my Isomac Tea home machine is still chugging away for eight years with two water backflushes daily and one Purocaffe flush every other week.

My commercial experience is mostly what I've seen at FOE. Only pump I ever saw there that was finally in need of replacement was at their main shop on Pearl Street - but that pump was used seven days a week with flushes every day for over ten years before it needed service.

Perhaps more to the point - a flush that's longer than five to ten seconds doesn't buy you anything additional in terms of results. The initial blast of pressure and the movement back through the system after pressure release is what does the work - I can't imagine how extended duration would make a difference.